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Posted by Jonathan Sturges on February 22, 2005, 11:48 am
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Walter Roberson wrote:
> :In a SuperStack II 3300 switch (model 3C16980), firmware 2.71, there are
> :untagged and tagged VLANs. Am I correct to assume that ports defined in
> :an untagged VLAN are partitioned off from other ports, into their own
> :broadcast domain?
>
> Yes, but...
>
> : What will the switch do with packets destined for a
> :host not in the untagged VLAN? Will it forward? I can see in the admin
> :GUI where you can control forwarding of tagged packets but nothing
> :specific to untagged.
>
> Tagged or untagged is not a property of the VLAN, but rather a
> property of a port. Unless 3Com is using terminology a very different
> way than everyone else, all ports, tagged or untagged, that are
> given the same VLAN number will be in the same broadcast domain;
> the ports that are marked as tagged will actually send the tag
> number as part of the packet when emitting a packet on the port,
> whereas ports that are marked as untagged will strip the tag number
> before emitting a packet on the port.
>
> Tagged ports are used when mostly communicating between switches (or
> between switches and routers), and untagged ports are mostly used for
> communicating with hosts; most hosts are not able to process the
> tag number [but it is becoming increasingly common to be able to.]
>
> Often a tagged port will be marked as being part of several VLANs;
> packets for all those VLANs can be sent on the same port, with
> the tag number being used on the remote end to figure out what goes
> where.
>
Thanks for this very clear explanation. :)
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